feat: Adds support for custom keyboard pages and other customizations

[Sub6Resources]

Description

• BREAKING: bool secondPage has been replaced with int page in MathFieldEditingController to allow for more than two pages.
• Adds support for custom keyboard pages using the new customPages attribute that takes a list of CustomButtonPages.
  • Each CustomButtonPage takes a List<List<KeyboardButtonConfig>> as well as an optional label or icon to be shown using the PageButtonConfig.
  • The existing pages were wrapped in this class.
• Adds a fontSize attribute to MathKeyboard and a keyboardButtonFontSize attribute to MathField to allow the font size of the keyboard buttons to be adjusted.
• Adds a heightFactor attribute to KeyboardButtonConfig to allow for customization of the height of keyboard rows.
• Adds widget tests for MathKeyboard to test the functionality of custom and default pages on the keyboard.

Related issues & PRs

None

Checklist

• I have made myself familiar with the CaTeX
  contributing guide.
• I added a PR description.
• I linked all related issues and PRs I could find (no links if there are none).
• If this PR changes anything about the main math_keyboard or example package
  (also README etc.), I created an entry in CHANGELOG.md (## UPCOMING RELEASE if the change
  on its own is not worth an update).
• If this PR includes a notable change in the math_keyboard package, I updated the version
  according to Dart's semantic versioning.
• If there is new functionality in code, I added tests covering all my additions.
• All required checks pass.

[github-actions]

Hi 👋🏽 Thank you for opening your first PR with simpleclub/math_keyboard ❤

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In the meantime, please check our contribution guidelines, the PR checklist, and the PR checks.

[edhom]

@Sub6Resources Thanks Matthew for the contribution😍 And sorry for the late review! I have just some nits but happy to merge this one then:)

[edhom]

Suggested change

	final List<CustomButtonPage>? pages;
	final List<CustomButtonPage> pages;

I think this can't be nullable anymore

[edhom]

Suggested change

	else if (type ==
	MathKeyboardType.expression)
	standardKeyboard,
	if (type == MathKeyboardType.expression)
	functionKeyboard,
	if (type == MathKeyboardType.expression)
	standardKeyboard,
	functionKeyboard,

[edhom]

Suggested change

	...(widget.customPages.fold<List<List<KeyboardButtonConfig>>>(
	[],
	(previousValue, customPage) {
	return previousValue..addAll(customPage.buttonLayout);
	},
	)),
	for (final page in widget.customPages)
	...page.buttonLayout

Could you check if this works?🙂

[absar]

@Sub6Resources @edhom this is a very useful PR can it be merged

[CLAassistant]

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